The Japanese love their seafood raw. The fresher and livelier it is, the better.
Katsu ika odori-don or dancing squid rice bowl is a meal that has fresh squid atop either noodles or rice. The squid then squirms when one pours soy sauce on it.
Don’t worry, the food isn’t alive. The squid “dancing” is what happens when sodium in the sauce reacts with the muscle, in the same manner frog legs twitch when being seasoned.
To prepare the dish, a live squid’s head is removed, and its body is placed on top of rice and noodles, with salmon eggs and other ingredients. The squid appears lifeless, that is until soy sauce or other sodium-rich liquid is added.
Sodium chloride activates the muscle which makes the squid wriggle momentarily.
A more in-depth scientific explanation, the increased concentration of sodium ions causes neurons adjacent to muscles in the tentacles to fire. These neurons cause calcium concentration to increase in muscle cells, together with adenosine triphosphate (ATP), results in muscle contractions.
Occasionally, the movement is intense enough for the squid to escape the bowl. Afterward, the body is sliced and placed back on the dish.